Road Trip to Peridot

Before I tell you about my road trip, let me answer the most common question I hear about peridot: is it pronounced per-ə-ˌdät or per-ə-dō(t)?!  As my father would say, the answer is “yes”.  Both pronunciations are correct.

I recently took a road trip to the town of Peridot, Arizona (locally pronounced per-ə-ˌdät).  Peridot Mesa is the premier location for mining the gem in the United States.

The peridot mine is located on the San Carlos Apache Indian Reservation.  Collecting in this area is very strictly regulated; you must obtain a permit and even then you can only access the area when guided by a claim holder.  Once at the mine, you must remain on the claim owned by your guide.  I was able to visit the mine with Stevie Joey, who has been mining his family’s claim for many years.  Most of the work is done using a jack hammer, but larger equipment is brought in to move overburden material and open new locations.

The peridot crystals are found in peridotite xenoliths (say that 10 times fast).  Xenoliths are pieces of preexisting rock that are ripped out of place as molten magma moves through the depths of the earth.  The earth’s upper mantle consists of peridotite, a rock composed of olivine as well as several other minerals.  The magma picked up pieces of peridotite and carried them to the surface.  The heat of the magma started to melt the rocks resulting in the rounded edges of the inclusions (see photo below left).  Olivine is the green mineral in peridotite and when it’s found in gem quality (good color and clarity), it is known as the gem peridot.  The peridotite at the mine is very crumbly which is why there’s so much green sand around.  The rock surrounding the peridotite xenoliths is basalt – the rock that forms when lava cools.  So what we’re seeing here was part of the earth’s mantle – pretty darn amazing!

Most of the pieces of peridot I found were very small, but larger pieces can be found.  I tried to remove the large dark crystal in the photo above right, but it was internally fractured and didn’t make it out in one piece.  I came home with a few nice samples of peridotite, but no large pieces of peridot.  An opportunity to see one of the world’s most interesting source of gems was an adventure worth having!

References & Resources:

Pronunciation:
https://www.merriam-webster.com/dictionary/peridot

About the area:
https://www.youtube.com/watch?v=6Pp2rydb8cI
https://en.wikipedia.org/wiki/Peridot_Mesa
To visit, contact Stevie Joey: http://www.peridotdreams.com/

Peridot and peridotite:
https://mochisgifts.com/2015/08/02/peridot/
https://minerals.usgs.gov/minerals/pubs/commodity/gemstones/sp14-95/peridot.html
https://www.gia.edu/peridot
https://www.mindat.org/min-48407.html
https://en.wikipedia.org/wiki/Peridotite

Photos (c) 2018, J. Fenton

Polymorphs: Marcasite & Pyrite

Polymorphism is one of the many fascinating properties of some minerals.  Polymorphs are minerals with the same chemical formula but different internal arrangement of  molecules.  This results in different external crystal shapes (called “habits”).    The resulting mineral depends mostly on the combination of temperature and pressure that were present at the time of formation.  A polymorph pair that may be familiar to you is diamond and graphite.  Both are composed of a single element, carbon (C), but crystallize very differently as shown below.

stock-photo-the-crystal-structures-of-diamond-and-graphite-two-of-polymorphs-of-carbon-611188460

 

This example shows you how very different polymorphs can be, both in how they look and in their physical properties; graphite has a hardness of 1-2 on the Moh’s Scale while diamond is 10.  Another polymorphic gemstone that I use in  jewelry is kyanite (Al2SiO5): both andalusite and sillimanite are  polymorphs.

Marcasite and pyrite are also polymorphs with the chemical formula FeS2  (iron sulfide).  Both have a hardness of 6-6 1/2, however marcasite crystallizes in the orthorhombic system while pyrite is isometric. In addition, marcasite crystals are not very stable so it turns out that marcasite jewelry is almost always made from pyrite.  I guess the name “marcasite” sells more jewelry than “pyrite”!

pyrite_1_V2

Natural pyrite cubes and assorted pyrite beads from my collection.

Pyrite is one of the best known minerals – almost every child has a piece in their rock collection.  Pyrite crystals can occur as near perfect cubes, or as pyritohedrons.  Pyrite is often called “fool’s gold” for it’s bright brassy color and metallic luster.  Next to real gold, the difference is obvious, but if you’re out mineral hunting and a piece of pyrite sparkles in the sun, it’s easy to be confused. As mentioned above, pyrite has a hardness of 6-6 1/2 while pure gold is only 2.5. Pyrite is an iron mineral so it is relatively heavy.

 

Lapis lazuli is a rock composed of three minerals, lazurite, pyrite, and calcite.   I enjoy using pyrite as an accent to bring out the pyrite included in lapis lazuli (and it looks great with azurite and other gems too).

Pyrite should not be cleaned with water; clean it with a soft cloth. Over time, pyrite may tarnish or dull and can leave black residue, so you may not want to wear it over light colored fabrics.

Now you won’t be a fool when choosing jewelry with pyrite!

References:
https://www.gemselect.com/other-info/marcasite-pyrite.php
https://www.mindat.org/min-2571.html
https://www.mindat.org/min-3314.html

Malachite

Malachite has always been one of my favorite gemstones for jewelry so I’m not sure what took me so long to get around to telling you about it!

Mala_n_1

Malachite necklace on malachite specimen with silky texture.

Malachite is a relatively common mineral associated with oxidized copper veins. It has the chemical formula Cu2(CO3)(OH)2. Malachite is easily recognized by the beautiful color banding of shades of bluish-green to darker green and almost black. Mineral specimens can be found showing many different habits; commonly botryoidal (rounded grape-like masses) with fibrous or silky structure, small crystals, stalactites, and tufts.

azur_mal_p

Azurmalachite pendant.

Although malachite can be a minor ore of copper, it is mostly used for jewelry and carvings. It is commonly found in combination with other minerals; for jewelry use, azurite (azurmalachite), chrysocolla, and shattuckite often show up in the mix.

 Historically, large quantities of malachite came from Russia, but this supply has been mostly exhausted. Currently, malachite is mined in Australia, Chile, the Democratic Republic of Congo, France, Namibia, the United States (Arizona), and Zimbabwe.

Knowledge of malachite goes as far back as the ancient Egyptians, Greeks, and Romans where it was used for jewelry, eye shadow, and as a pigment for paints. Paint using malachite has been found in Egyptian tombs and in European paintings from the 15th and 16th centuries. A stunning use of malachite can be seen at the Winter Palace at the Hermitage Museum in St. Petersburg, Russia,  which features “the Malachite Room” with  ornamental columns, vases and fireplace panels made from malachite.

There are both synthetic and imitation versions of malachite. With a little practice, they can be easily recognized.

Malachite is very soft (3.5 – 4 on the Moh’s Scale of Mineral Hardness) and scratches easily. It is also sensitive to chemicals and is sometimes coated with resin or wax to help protect it. Malachite necklaces and earrings are less likely to incur damage than rings or bracelets. Malachite jewelry should be cleaned with mild dish soap and water and a soft brush. Do not use steamers or chemical or ultrasonic cleaners as they can damage the stone and/or remove any protective coatings.

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Malachite earrings.

Every piece of malachite is unique and a wonderful addition to your jewelry collection!

References:
https://www.mindat.org/min-2550.html
https://www.gemselect.com/gem-info/malachite/malachite-info.php
https://geology.com/minerals/malachite.shtml
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York.

Moonstone and Rainbow Moonstone – Same Mineral, Different Gems!

Today I’m going to discuss the similarities and differences between labradorite, moonstone, and rainbow moonstone. I’ve noticed that most customers who ask for moonstone jewelry really mean rainbow moonstone, they just don’t know it!

All three of these gems are part of the feldspar group of silicate minerals that have a hardness of 6 – 6 1/2 on the Moh’s scale. Feldspar is a very common rock forming mineral, but it has a range of chemical composition leading to many different varieties of minerals in this group.  Within the chemical formula of feldspar, several different elements can be substituted in part or completely by another element. Only a few of the many different feldspar minerals are rare or beautiful enough to be considered gems.

All three gems show “phenomena”; special optical effects due to how they transmit and reflect light.  Read more about the different phenomena mentioned below in these blog posts: Part 1, Part 2.

Labradorite:

LASSN104_a

Labradorite pendant and beads showing labradorescence

Labradorite is classified as a plagioclase feldspar with the chemical formula (Ca,Na)[Al(Al,Si)Si2O8]. This formula shows that there can be some variation in the relative proportions of calcium and sodium, and aluminum and silica, and still be classified as labradorite.

 

 

Labradorite was named for where it was discovered, Labrador, Canada. What makes this gem special is the phenomenon of “labradorescence” (great originality in naming). Without direct light, the gem generally appears gray. In the light, vibrant blues and greens flash across the surface. Sometimes gold, pink, or other colors are also seen; the name “spectrolite” is sometimes used in this case.

Moonstone:
Moonstone is the gem form of the mineral orthoclase (potassium feldspar, sometimes

MOGFN102_a

Some of the colors of moonstone.

called K-spar) with the chemical formula ‎KAlSi3O8.  

Common colors include white, gray, and orange. Less commonly seen are yellow or brown. Moonstone’s phenomenon is called “adularescence” which gives the gems a whitish sheen or cloud that appears to float within the stone. This sheen, which appears to some to look like the moon shimmering in the sky, is the source of the name.

Rainbow Moonstone:

MOGVN101_a

Rainbow moonstone (labradorite).

Here’s the chemical formula for rainbow moonstone: (Ca,Na)[Al(Al,Si)Si2O8]. It’s exactly the same as labradorite because … rainbow moonstone is actually a variety of labradorite!

Rainbow moonstone can be transparent to translucent white. Rainbow moonstone also shows adularescence, but the sheen is blue, sometimes with other colors, and is caused by the same mineral structure that causes labradorescence.

All three gems are feldspars and all are beautiful – their differences are just a matter of chemistry. My favorite of the three is labradorite. What’s yours?

References
GIA Gem Identification Lab Manual, May 2012.
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York.
https://www.mindat.org
https://www.gemdat.org
https://www.gemselect.com

All photos © J. Fenton, Mochi’s Gifts, 2018

Topaz

Topaz is one of November’s birthstones (citrine is the other), but it is not as well known as many other birthstones. This may possibly be because many people think of drab yellow or brown hues when they think of topaz. I hope to remedy that misconception here, not least of all because it’s MY birthstone!

GENERAL INFORMATION:
Topaz has the chemical formula Al2(F,OH)2SiO4 and grows in long prismatic crystals. Well formed crystals often show a characteristic “chisel point”.  Although topaz is one of the hardest gemstones at 8 on the Moh’s Scale of Mineral Hardness, it is not very tough and is susceptible to breakage from impact or temperature changes. It’s best used in earrings and necklaces and should be worn in protective settings such as bezels when used for rings.

Topaz is found in many countries including the United States, China, India, Myanmar, Russia, Sri Lanka, and Vietnam.  Commercial mining areas include Brazil, Madagascar, Namibia, and Pakistan.

Topaz_crystal_a

Topaz crystal from Utah showing “chisel point” termination.  Photo (c) J. Fenton, 2017

COLOR:
Besides yellow and brown, topaz occurs naturally in orange, pink, purple, red, light blue and light green as well as colorless crystals.  Orangey-red to pink gems may be called Imperial Topaz and are among the most valuable colors.

Sap_top_b

Sapphire and blue topaz necklace. Photo (c) J. Fenton, 2017

TREATMENTS:
Blue topaz: Prior to researching this article, I was unaware of naturally occurring blue topaz. It’s quite rare and most blue topaz found in jewelry comes from colorless material that has been irradiated and heated.  There are several methods of treatment; for more information read this article.  The combination of heat and irradiation results in a range of blue colors; “Swiss blue” and “London blue” are two common trade names.  The treatment is stable and permanent.

Mystic topaz: Colorless topaz is enhanced with a thin covering of an iridescent film.  This gives the gem a beautiful display of different colors as you move it in the light. The treatment is not permanent; the film can be scratched or polished off.  Care should be taken to avoid abrasion to the surface when wearing this gem.

CARE:
Clean your topaz jewelry in warm soapy water; don’t use steamers or ultrasonic cleaners.

References:
https://www.gia.edu/topaz
http://4cs.gia.edu/en-us/blog/november-birthstone-topaz-and-citrine/
https://www.gemselect.com/gem-info/mystic-topaz/mystic-topaz-info.php
https://en.wikipedia.org/wiki/Mohs_scale_of_mineral_hardness
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York.

Do you know Beryl?

Pure beryl (Be3Al2Si6O18) is colorless and is known as “goshenite“.  Beryl is a gem species; the addition of trace elements can result in one of its many varieties including:

Emerald – May’s birthstone is colored by chromium or vanadium and is the most valuable of the beryls.  Emeralds are medium to dark bluish-green to yellowish-green.  Light colored gems are referred to simply as “green beryl“.  Emeralds commonly have many inclusions and fractures so large gems are uncommon.  Most commercially mined emeralds come from Colombia, Zambia, Brazil, and Zimbabwe.  Emeralds can be found in the United States in North Carolina.

Cristaux de bŽryl var. Žmeraude sur gangue (Colombie)

Emerald crystals (Photo: public domain)

Aquamarine – March’s birthstone gets its blue color from iron.  Aquamarines are light blue-green; medium to dark blue gems are known as “maxixe beryl“.   Large clean aquamarine gems are common.  Aquamarine is mined in Brazil, Nigeria, Zambia, Mozambique, Madagascar, Pakistan, and Vietnam.  In the United States, aquamarine can be found in Colorado, Idaho, and Wyoming.

aqua_rm_am_b

Aquamarine, rainbow moonstone and amethyst necklace (Photo: J. Fenton 2017)

Morganite -Manganese gives morganite its pink to peach color.  This lesser known beryl has been gaining in popularity in recent years.  It was discovered in 1910 in Madagascar and was named for the financier J.P. Morgan.  The gem is also found in Brazil, Afghanistan and Mozambique.  Morganite has been found in California and Maine in the United States.

Heliodor (also Golden or Yellow Beryl) – Heliodor is generally considered a collectors gemstone and is not often found in jewelry.  Traces of iron cause the greenish-yellow to orangy-yellow color.

Red Beryl (Bixbite) – Red beryl is quite rare and has been found only relatively small crystal sizes.  Manganese provides the red color which is very saturated in this gem.  It is  found in the United States in Utah and small crystals have also been found in New Mexico.

Of the varieties above, I’ve seen beads made from emerald, aquamarine, morganite, and green beryl.  So now you know beryl!

References:
https://www.gia.edu/gia-gem-project-beryl
https://www.gia.edu/gem-encyclopedia

http://geology.com/minerals/beryl.shtml
GIA Gem Identification Lab Manual, May 2012
https://en.wikipedia.org/wiki/Beryl

 

8 Ways to Clean Out Jewelry Clutter

I recommend looking through your jewelry once a year and pulling out pieces you no longer wear.  As a first step, take the time to clean the jewelry well; sometimes this will be enough to make you love it again (and if not, clean jewelry will help you with your next steps).  Consider why you don’t wear it, then take a look at the list below and take action. 

1. FIX it:
  For beaded jewelry, your local bead shop may have staff who offer repair services.  In addition, some bead shops have workshop hours when customers can do their own repairs using store tools and staff assistance.  I offer restringing services; contact me for more information. 

For gold, platinum, or silver jewelry, check with your local jewelry store.  Many stores offer on-site repairs  or send work out to a repair service.  Easy fixes include replacing clasps or re-soldering pieces together.  There is a “blue book” that provides guidance for pricing of jewelry repairs.  Not all jewelry stores use it, so be sure to get an estimate for any work you’d like done. 

Costume jewelry (plated or non-precious metals) may not be worth repairing unless it has strong sentimental value.

2. REDESIGN it:  Do you have heirloom or sentimental pieces that are not your style?  Jewelry that’s too long or too short?   Consider adding, replacing, or removing components to change the look to something you would enjoy wearing. A redesign may also offer the opportunity to make matching earrings or bracelets from leftover parts.  Again, your local bead shop or jewelry store would be a good place to start.  I am also happy to work with you to redesign beaded jewelry.

3. TRADE it:  Get your friends together for a jewelry party.  Everyone brings the jewelry they don’t wear and you can trade with each other.   

4. SELL it:  First, research the value of your items.  For fine jewelry, consider getting an  appraisal You can look at prices for similar jewelry on websites like eBay, but keep in mind “asking” prices may be higher than the actual sale price.  Remember that you’re selling your jewelry second-hand, not new, no matter what the condition of the piece is.

You can sell your jewelry on-line yourself (eBay or Craig’s List are some options) and there are also services that will sell your items on-line for you.  You will need good quality photos of each piece of jewelry.  Most services charge a fee either for listing an item or when the item is sold.  You may also incur mailing and insurance costs to ship the items.  If you’re selling person to person, be sure to consider your personal safety before meeting with potential buyers. 

Depending on the age and quality of the jewelry, you may be able to sell it to a business specializing in antique or estate jewelry, or to a pawn shop.  A buyer will inspect your jewelry and may test the metals and/or gems.  Keep in mind that the price they pay you must be low enough that they can resell the jewelry at a profit.  

5. CONSIGN it:  Consignment stores sell your jewelry for you at their location and keep a portion of the profit.  Check your local stores for what types of items they accept and their payment terms.

6. DONATE it:  Fine jewelry can be donated to a charity for fundraising or auction events.  Be sure to get an “appraisal for donation purposes” for tax purposes.  Costume jewelry can be donated to your local charity, thrift store, or school drama program.  Donations to qualified organizations may be tax deductible so request a receipt.

7. SCRAP it:  You can sell gold, silver, and platinum jewelry for its melt value.  When scrapping jewelry, diamonds may have limited resale value; most other gemstones generally don’t.   A reputable scrap buyer will make their offer based on a percentage of the “spot price” of the metal for that day.  It may be desirable to check offers from 2-3 businesses to see who is paying the highest rate.  Remember that precious metals used in jewelry are generally not pure (see my blog about gold here); you’ll only be compensated for the actual weight of the desired metal.

8. TRASH it:  If it’s not made of a precious metal, not repairable, and not appropriate for a donation, it may be time to toss it in the trash.

Fill your jewelry box with pieces you love and pass the rest along for someone else to enjoy! 

How Much is my Jewelry Worth?

How much is my jewelry worth?  I’m asked this at every show.  As a gemologist I can identify the gemstones in your jewelry, but to answer the question of value, the right person to ask is an appraiser.  I’ve asked my colleague, Jeanne Hawk, a GIA Graduate Gemologist, Registered MasterValuer and Certified Insurance Appraiser, to be a guest blogger this month:

Establishing and substantiating the value of an item are what appraising is all about. An appraisal is an opinion of value, a well-researched conclusion that is supported by facts which are interpreted from the marketplace. Most jewelry appraisals are done for obtaining insurance coverage. An insurance appraisal is used to determine the retail replacement value of a jewelry item. Other appraisal types include those done to determine fair market value for estate items and items sold for scrap value.

Many of my clients have jewelry of unknown identification or value. I do consultations to identify the gemstones and/or diamonds and metal karatage to determine what you have and whether you should keep it, insure, or scrap it, as is often the case with outdated gold chains. I’ll let you know the market value if you plan to sell it. And if it’s something you want to insure, I can prepare an appraisal for you.

There are six steps involved in the appraisal process as follows: 1) establish the scope of the appraisal, 2) plan the appraisal, 3) collect and analyze the data, 4) apply a valuation approach, 5) set limitations and contingency conditions, and 6) supply the final estimate of value.

At the present time anyone can call oneself a professional jewelry appraiser. However, self-anointing does not confer expertise. The key is education. A gemologist who has undergone formal gemological training, holds a degree or special education in valuation science, and has buying and selling experience either on a wholesale or retail level has the basic prerequisites of an appraiser. The valuation must be done by an individual with suitable qualifications who has no interest (no bias) in the item. Participation in professional appraising organizations is important, as well. It is critical that any jewelry appraisal be developed and written in accordance with the Uniform Standards of Professional Appraisal Practice (USPAP), authorized by Congress as the source of appraisal standards and appraiser qualifications.

I am a certified Gemoljeanne_cropogical Institute of America (GIA) Graduate Gemologist (GG), qualified to accurately identify and grade the gemstones in your jewelry. As a Registered Master Valuer™ and Certified Insurance Appraiser™, I am trained in appraisal valuation techniques and can appropriately value and appraise your jewelry. All appraisal reports are prepared in accordance with USPAP.

At your appraisal appointment, I will clean, identify, measure, weigh, grade, and photograph your jewelry. Most appointments take 30 minutes; longer appointments may be needed for multiple items. You will leave with your jewelry. In 7-10 business days, once I have completed the valuation part of the appraisal, you will receive your appraisal via email. Payment for the appraisal, and any hard copies requested, is due at the time of your appointment. Would you like to learn more about how the value of jewelry is determined? Find out in my FREE report! Call this 24 hour toll free recorded message to request your report. 1-800-579-3932.

Jeanne Hawk Fine Jewelry Appraisals specializes in gem identification, diamond grading, jewelry appraisals, market value estimations, general consultation, and quality assessments. To best meet my clients’ needs, services are provided by appointment only. I can be reached at 831-359-3449 or via email at info@hawkjewelryappraisals.com to schedule an appointment. The office is located at 5521 Scotts Valley Drive, Suite 235, Scotts Valley, CA 95066. The company website is http://www.hawkjewelryappraisals.com. Give me a call or visit my website today!

 

Where do the gemstone beads in your jewelry come from?

I’m asked this question at every show.  It’s a great question but I can’t always answer it. Here’s why:

Some gems come almost exclusively from one area; fossil “turitella agate” comes from Wyoming in the U.S. and tanzanite from Tanzania, Africa. But most gems are found and mined in more than one location. For example, lapis lazuli comes from Afghanistan, Pakistan, Russia and Chile.

LLGFN104_a

Lapis lazuli from Afghanistan (with malachite and gold-filled beads, item LLGFN104

 

In some cases, especially beautiful specimens of a  gem are found in specific locations; Burmese rubies are highly prized.  Because of this, some beads are sold with their source location as part of their name; Ethiopian opal and Australian boulder opal beads are examples.

While some rough (uncut gem material) is cut and polished as gems, beads or carvings in the country where it was mined, most goes to major “cutting centers” in other countries. China and India are the biggest cutting centers for beads. Both locations produce great beads; beads from India are generally hand-made and Chinese products are often laser or machine-made. Because making rough material into beads is where the “value” is added, most beads come with labels saying they were made in the country where the cutting center is located rather than where they were mined.

So, when my beads are labeled as being from China or India, I don’t know the location of origin. But when a gem comes from only one location or when I buy directly from an importer, I know the source.

FTGVE102_Nov15_a

Turitella agate fossils from Wyoming (with garnet and gold-filled, item FTGVE102)

Kyanite

With a range of blue hues in a single stone, kyanite is a fabulous gem for beautiful and unique jewelry.  Kyanite has a particularly unique and interesting property: it has two  different measures of hardness in the same crystal.  A gem’s hardness is defined as its resistance to scratching and is usually stated as a single number or small range; diamond is 10 on the Moh’s hardness scale, quartz is 7.  When you look at a kyanite crystal,  it may appear to have a grain like a piece of wood; the hardness can be 5-5 1/2 in the direction of the grain and 7 across it.

Kyanite is nKYSSN102_aamed from the Greek word for dark blue, kyanos, from which we get “cyan” as a shade of blue.  Most kyanite is blue, but it can also be white, gray, orange, yellow and green.  Although still not very common in jewelry, good quality blue and green material is used for beads and cut stones.

Kyanite crystals grow in long flat “blades”.  The gem can be translucent to opaque and the color is often very unevenly zoned over the crystal.  It is a metamorphic mineral with chemical formula Al2SiO5.   It is also a “polymorph”; one of three minerals with the same chemical formula but different crystal structure (the other two minerals are andalusite and sillimanite).

Kyanite  can be found in many locations around the world including Austria, Burma, Brazil, Cambodia, India, Kenya, Myanmar, Nepal, Russia, Serbia, Switzerland, Tanzania, the United States and Zimbabwe.  Besides jewelry, kyanite is used in the manufacture of porcelain, spark plugs and  electronics.

Kyanite is fairly durable, but KYGVE102_16_ahas perfect cleavage that can cause the stone to split with a single hard knock or blow. Don’t use ultrasonic cleaners, steamers, bleach or other harsh chemicals when cleaning kyanite; use water and a mild soap.

References:
Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York.
Gemological Institute of America, Gem Identification Lab Manual, 5/2012
http://www.gemselect.com/gem-info/kyanite/kyanite-info.php